In previous work, we isolated and characterized a mouse cDNA clone encoding a new transmembrane protein belonging to the EGF-like superfamily. The predicted protein product of this cDNA (termed delta- like or dlk) contains 385 amino acids and is highly homologous to invertebrate homeotic proteins, including Delta, Serrate, and Nothch of D. melanogaster; lin-12 and glpl of C. elegans, and uEGF1 of the sea urchin. All these homeotic transmembrane proteins contain several EGF- like repeats at the extracellular domain which intervene in protein- protein interactions between cells. These interactions generate signal transduction events during normal or tumoral development which are involved in differentiation decisions. Our objectives for the year, were to obtain and characterize a human dlk clone, as well as to produce antibodies against the dlk protein. To fulfill the first objective we used two strategies. First, mRNA expression studies showed that dlk was expressed in Small Cell Lung Cancer, Neuroblastomas and, in normal tissue, almost exclusively in human adrenal gland and placenta. We screened a human adrenal gland cDNA library by using mouse dlk as a probe. Following this approach, we were able to obtain two cDNA dlk clones, that, however, were only partial. To obtain a full length human dlk, we decide to use a PCR based strategy. Computer analysis of the dlk sequence allowed the design of two oligonucleotides to be used for PCR amplification of human adrenal gland cDNA. This approach was successful.